Legislation passed after the 2007 Virginia Tech shooting was supposed to ensure that anyone with a record of severe mental illness couldn't purchase guns. But many states are not submitting the requested information to establish the database.

This issue is getting renewed attention in the wake of the Newtown, Connecticut, shootings, as part of a national conversation on avoiding further tragedies.

Any individual who has been involuntarily committed or been ruled mentally incompetent by a court is banned from buying a gun and should be listed in the national background check database. But those records are spotty.

In theory, a shopper could be barred from buying a gun in Pennsylvania, but travel to another state to purchase it.

In 2008, the federal government offered more than $1 billion in aid to states to update these databases, but there hasn't been much progress. Pennsylvania officials, for instance, have cited technical problems as the holdup - as well as confusion over exact registration requirements.

Shira Goodman, who directs the advocacy organization Ceasefire PA, says her group is trying to put pressure on Pennsylvania legislators to begin submitting the records.

"It is really a matter that should be able to be resolved, that shouldn't have taken this many years," she said. "We have asked the state police and the governor to look into it, and again, our only answer has been 'legal technical problems.'"

Earlier this year, New Jersey started to upgrade its flow of mental illness-related records to the national database, entering about half-million paper records dating to 1975 by the end of this year.